From the Neuromuscular and Neurogenetics Disorders of Childhood Section (A.R.F., P.Y., M.E.L., S.B.N., G.V.A., Y.H., L.H.H., S.D., D.X.B.-G., Y.Z., M.F., J.D., C.M., C.A., C.G.B.), Neurogenetics Branch, NINDS, NIH, Bethesda, MD; Division of Neurology (M.E.L.), Oregon Health and Science University, Portland, OR; Department of Neurology (L.H.H.), Boston Children's Hospital, MA; Rehabilitation Medicine Department (M.S.J., M.W.); Occupational Therapy Section (R.P.), Rehabilitation Medicine Department, NIH, Bethesda, MD; Division of Neurology (D.X.B.-G.), Children's National Hospital, Washington, DC; Division of Pulmonology (O.M.), Children's Hospital of Philadelphia, PA; Santhera Pharmaceuticals (R.H., D.P.), Pratteln, Switzerland; and Department of Biostatistics (K.C.), Mailman School of Public Health, Columbia University, NY.